From the Guidelines
PET/CT is the preferred imaging modality over conventional CT with contrast for the workup of vasculitis, particularly for large-vessel vasculitis, due to its ability to detect early inflammatory changes and assess disease activity with high sensitivity and specificity. According to the most recent study by 1, FDG-PET should be considered the first imaging alternative to ultrasound of extracranial vessels because of evidence supporting a high diagnostic value. The study highlights that FDG-PET has a sensitivity of 76% and specificity of 95% for diagnosing vasculitis, making it a valuable tool for detecting metabolically active inflammation throughout the body.
Some of the key advantages of PET/CT over conventional CT with contrast include:
- Detecting early inflammatory changes in vessel walls before structural damage occurs
- Providing better assessment of disease activity and extent
- Highlighting metabolically active inflammation throughout the body in a single examination
- Being particularly valuable for large-vessel vasculitis like giant cell arteritis and Takayasu arteritis
However, it's essential to consider the limitations of PET/CT, including higher radiation exposure, greater cost, limited availability, and reduced utility for small-vessel vasculitis. Conventional CT with contrast remains valuable for detecting structural changes and complications like aneurysms or stenosis, but PET/CT's ability to detect functional metabolic changes before anatomical alterations makes it increasingly important in vasculitis evaluation, especially when diagnosis is uncertain or disease activity assessment is needed, as supported by 1.
In terms of specific diagnostic performance, a study by 1 compared CTA with FDG-PET/CT and found that the sensitivity and specificity of CTA for diagnosing GCA were 73% and 78%, respectively, while FDG-PET/CT demonstrated a strong correlation with inflammatory markers. Another study by 1 reported that ultrasound of temporal arteries revealed a higher sensitivity than FDG-PET, while FDG-PET performed better at subclavian and carotid arteries.
Overall, the evidence suggests that PET/CT is a valuable tool for the workup of vasculitis, particularly for large-vessel vasculitis, due to its ability to detect early inflammatory changes and assess disease activity with high sensitivity and specificity.
From the Research
Advantages of Pet CT over Conventional CT with Contrast
- Pet CT has been shown to be a powerful prognostic marker by allowing identification of patients at risk of vascular complications 2.
- It allows early detection of inflammation, before morphological and irreversible vascular changes can be observed, enabling prompt diagnosis and treatment of large vessel vasculitis (LVV) 2.
- Pet CT has a high sensitivity for inflammatory activity, making it useful in the diagnosis of active vasculitis 3, 4, 5.
- It can reliably detect the earliest changes of disease improvement post-therapy, and persistent activity is an indicator of non-responders to therapy 5.
Diagnostic Accuracy
- [18F]FDG-PET/CT and 3D-T1w TSE-MRI have both been shown to have high diagnostic accuracy of 88% and 83%, respectively, in the diagnosis of active large vessel vasculitis and single-organ vasculitis of the aorta 3.
- The diagnostic accuracy of Pet CT is even optimized by combining it with MRI, with an accuracy of 95% and a high positive predictive value (92%) and negative predictive value (100%) when both modalities show concordant findings 3.
Monitoring Disease Activity and Response to Therapy
- Pet CT can be used to monitor disease activity and response to therapy in patients with large vessel vasculitis, with changes in FDG uptake reflecting changes in disease activity 5, 6.
- However, the role of Pet CT in predicting disease relapse during follow-up is less obvious, as vascular FDG uptake can be detected in the absence of clinical or biochemical signs of disease activity 6.